Solid oxide fuel cell

ABSTRACT

A single cell for a fuel cell in which an air electrode or a fuel electrode includes at least two layers. The air electrode includes an adhering cathode layer formed on one surface of the solid electrolyte layer and configured to show a function to allow the air electrode and the solid electrolyte layer to adhere electrically and mechanically to each other, and an electricity collecting cathode layer formed on the adhering cathode layer and configured to show an electricity collecting function of the air electrode. Alternatively, the fuel electrode includes an adhering anode layer formed on the other surface of the solid electrolyte layer and configured to show a function to allow the air electrode and the solid electrolyte layer to adhere electrically and mechanically to each other, and an electricity collecting anode layer formed on the adhering anode layer and configured to show an electricity collecting function.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a solid oxide fuel cell (SOFC)which uses a solid electrolyte to obtain electric energy by utilizationof electrochemical reactions.

[0003] 2. Description of the Related Art

[0004] Fuel cells have recently attracted considerable attention as aclean energy source which is capable of high energy conversion andglobally environmentally friendly.

[0005] A solid oxide fuel cell (hereinafter referred to as “SOFC”) isone having a structure in which two electrodes consisting of an airelectrode (cathode) and a fuel electrode (anode) sandwich a solid oxideelectrolyte layer. Reactive gas containing oxygen is supplied to the airelectrode, and reactive gas containing fuel gas is supplied to the fuelelectrode. An electro chemical reaction occurs at a three-phaseinterface where the electrode, the reactive gas and the solidelectrolyte mainly contact. These electrode materials are required tooffer the following properties 1) to 3).

[0006] 1) To promote the electrochemical reaction at theelectrode/electrolyte interface (i.e. the interface between theelectrode and the electrolyte), the electrode materials have a structurewhich can obtain a large area of the three-phase interface formed by theelectrode material, the electrolyte and the reactive gas.

[0007] 2) The electrode materials have a structure which makes it easierto introduce the reactive gas into the electrode/electrolyte interfacethat is an electrochemical reaction field.

[0008] 3) The electrode materials offer low electric resistance toenhance electricity collecting performance as the electrode.

[0009] To satisfy the properties of the items 1) and 2), the electrodemust be porous, and to decrease its electric resistance, the electrodelayer must have a sufficient thickness.

[0010] Accordingly, in order to offer the above described properties ofthe 1) to 3), with respect to the conventional electrode material, itsmicro powders were processed to be pasty, and coated onto the surface ofthe electrolyte layer by use of a printing method and a dipping method,followed by baking. Thus, the fuel electrode and the air electrode,which are a porous single-layer having a sufficient thickness, arerespectively formed.

SUMMARY OF THE INVENTION

[0011] It is difficult for the conventional single-layered air and fuelelectrodes to satisfy the foregoing three requirements. This is becauseto acquire high electricity collecting performance, the film thicknessof the electrode must be thickened, however it is difficult to obtain asufficient electrochemical reaction field to occur a cell reaction, thatis, a wide area of the three-phase interface is impossible with thethick film thickness of the electrode.

[0012] In addition, the conventional air electrode and fuel electrodeare formed by use of paste mixed with inorganic adhesive made of glassas a main component, and the inorganic adhesive does not participate inthe electrochemical reaction or disturb the electrochemical reaction.Accordingly, to produce the electrochemical reaction more effectively,such an inorganic adhesive should not be mixed.

[0013] Furthermore, LSC (lanthanum-strontium-cobalt complex oxide) hasbeen recently used as an air electrode material of SOFC for a lowtemperature (below 800° C.) operation. Since the LSC offers both ofelectron conductivity and ion conductivity, oxygen as reactive gas candiffuse into the electrode. Accordingly, the LSC can cause anelectrochemical reaction necessary for a cell reaction not only at thethree-phase interface but also at the two-phase interface. However, whenYSZ (yttria-stabilized-zirconia) is used as a solid electrolyte, the LSCreacts with the YSZ at 1000° C. or more, resulting in deterioration ofcell performance.

[0014] The present invention was made in consideration for the foregoingsubjects, and a first object of the present invention is to provide asingle cell having an electrode structure which shows small electricalresistance, good adhesion, and can provide a large three-phase interfaceor a broad two-phase interface necessary for a cell reaction. A secondobject of the present invention is to provide a cell plate configured bylaminating the single cell. A third object of the present invention isto provide a method of manufacturing the same, and to provide a solidoxide fuel cell comprising the same.

[0015] To achieve the above objects, a single cell for a fuel cell ofthe present invention has a structure in which a solid electrolyte layeris sandwiched by an air electrode and a fuel electrode, and the airelectrode or the fuel electrode is configured by at least two layers.

[0016] A single cell according to a first aspect of the presentinvention, includes an air electrode formed of at least two layers. Theair electrode contains an adhering cathode layer formed on one surfaceof the solid electrolyte layer and configured to principally show afunction to allow the air electrode and the solid electrolyte layer toadhere electrically and mechanically to each other; and an electricitycollecting cathode layer formed on the adhering cathode layer andconfigured to principally show an electricity collecting function of theair electrode. The adhering cathode layer has a structure denser thanthe electricity collecting cathode layer, and configures a three-phaseinterface, in which an electrochemical reaction occurs, composed of thesolid electrolyte layer, reactive gas and the air electrode. Theelectricity collecting cathode layer has pores providing the reactivegas to the three-phase interface sufficiently.

[0017] A single cell according to a second aspect of the presentinvention, includes a fuel electrode formed of at least two layers. Thefuel electrode includes an adhering anode layer formed on the othersurface of the solid electrolyte layer and configured to principallyshow a function to allow the air electrode and the solid electrolytelayer to adhere electrically and mechanically to each other; and anelectricity collecting anode layer formed on the adhering anode layerand configured to principally show an electricity collecting function.The adhering anode layer has a structure denser than the electricitycollecting anode layer, and configures a three-phase interface, in whichan electrochemical reaction occurs, composed of the solid electrolytelayer, reactive gas and the fuel electrode, and the electricitycollecting anode layer has pores for providing sufficient reactive gasto the three-phase interface.

[0018] A cell plate for a fuel cell of a third aspect of the presentinvention is configured by two-dimensionally analyzing single cells forthe fuel cell of the present invention, and then these cells areprocessed to a united cell plate.

[0019] A fuel cell of a forth aspect of the present invention isconfigured by laminating the cell plate for the fuel cell of the presentinvention.

[0020] A method of manufacturing the single cell for the fuel cell of afifth aspect of the present invention, by use of any of a PVD method, aCVD method and a plating method, a solid electrolyte layer is firstformed and then an adhering anode layer is formed on one surface of thesolid electrolyte layer and an adhering cathode layer is formed on theother surface of the solid electrolyte layer. Furthermore, by use of oneof a spray coating method and a printing method, an electricitycollecting anode layer is formed on the adhering anode layer and anelectricity collecting cathode layer is formed on the adhering cathodelayer, followed by baking the electricity collecting anode layer and theelectricity collecting cathode layer after formation of the electricitycollecting anode layer and the electricity collecting cathode layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 A is a section view of a single cell according to a firstembodiment of the present invention, and FIG. 1B is an enlarged sectionview of a portion A in FIG. 1A.

[0022]FIG. 2 is a section view of a single cell according to a secondembodiment of the present invention.

[0023]FIG. 3A is a section view of a cell plate of a fuel cell accordingto embodiments of the present invention, and FIG. 3B is a perspectiveview of the cell plate of the fuel cell of FIG. 3A.

[0024]FIG. 4A is a section view of a single cell according to an example1 of the present invention, FIG. 4B is a section view of a single cellaccording to a comparative example 1, FIG. 4C is a section view of asingle cell according to a comparative example 2, and FIG. 4D is asection view of a single cell according to an example 3.

[0025]FIG. 5 is a table showing conditions and cell properties accordingto the examples 1 and 2 and the comparative examples 1 to 3.

[0026]FIG. 6 is a table showing conditions and cell properties accordingto examples 3 to 6 and comparative examples 2 to 7.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] Descriptions for a single cell and a cell plate of a solid oxidefuel cell according to each embodiment of the present invention will bedescribed in detail below. In this specification, the symbol “%”indicates a mass percentage unless specifically mentioned.

[0028] Furthermore, for the sake of convenience of explanations, onesurface of each layer such as a substrate and an electrode layer isdescribed as “upper surface” and the other surface is described as“lower surface”. However, these are equivalent constituent components,and, as a matter of course, constitutions in which these components arereplaced by one another are within the scope of the present invention.

First Embodiment

[0029]FIG. 1A shows a structure of a single cell according to a firstembodiment of the present invention. Also FIG. 1B shows an enlargedsection view of a portion A circled with broken line in FIG. 1A. Thesingle cell has the structure in which the solid electrolyte layer 10 issandwiched by the air electrode (cathode) 20 and a fuel electrode(anode) 30. The single cell of this embodiment has a feature in that theair electrode 20 and the fuel electrode 30 are respectively formed by atleast two layers, each of which has a different function.

[0030] To be concrete, as shown in FIG. 1A, the air electrode 20 has alaminated structure composed of an adhering cathode layer 21 formed onthe upper surface of the solid electrolyte layer 10 and an electricitycollecting cathode layer 22. The fuel electrode 30 has a laminatedstructure composed of an adhering anode layer 31 formed on the lowersurface of the solid electrolyte layer 10 and an electricity collectinganode layer 32.

[0031] The adhering cathode layer 21 in the air electrode 20 is onehaving a main function which adheres the air electrode 20 to the solidelectrolyte layer 10. Furthermore, the adhering cathode layer 21 in theair electrode 20 is one constituting a three-phase interface or atwo-phase interface that is an electrochemical reaction field requiredfor a cell reaction. The electricity collecting cathode layer 22 is onehaving a main function to collect electricity of the air electrode 20.

[0032] Similarly, the adhering anode layer 31 in the fuel electrode 30is one having a main function to adhere the fuel electrode 30 to thesolid electrolyte layer 10. Furthermore the adhering anode layer 31 inthe fuel electrode 30 is one constituting a three-phase interface thatis an electrochemical reaction field required for a cell reaction. Theelectricity collecting anode layer 32 in the fuel electrode 30 is onemainly having an electricity collecting function.

[0033] The adhering cathode layer 21 and the adhering anode layer 31offer electrically and mechanically high adhesion to the solidelectrolyte layer 10, and though the adhering cathode layer 21 and theadhering anode layer 31 are discontinuous, they should be a conductivelayer having a dense film structure, to obtain a sufficient three ortwo-phase interface.

[0034] On the other hand, to acquire a high electricity collectingfunction, the electricity collecting cathode layer 22 and theelectricity collecting anode layer 32 should be formed of anelectrically conductive layer having a sufficient thickness to reduceelectrode resistance. Furthermore, to supply sufficient reactive gas tothe three-phase interface where the cell reaction occurs, theelectricity collecting cathode layer 22 and the electricity collectinganode layer 32 should have a porous structure through which the reactivegas can pass.

[0035] As described above, by respectively constituting the airelectrode 20 and the fuel electrode 30 by a plurality of electrodelayers, each of which has a different function, it is possible to givegood electrode performance, which cannot be achieved by a single-layeredelectrode layer, to the air electrode 20 and the fuel electrode 30.Specifically, the adhering cathode layer 21 enhances adhesion of the airelectrode 20 to the solid electrolyte layer 10 more effectively, andforms the three or two-phase interface contributing to more cellreactions in the interface between the air electrode 20 and the solidelectrolyte layer 10. The electricity collecting cathode layer 22increases the electricity collecting performance more effectively, andmakes it easier to be electrically connected to the outside.Furthermore, the electricity collecting cathode layer 22 suppliesreactive gas more effectively to the three-phase interface that is areaction field where a cell reaction occurs. Since sufficient adhesioncan be obtained due to the existence of the adhering cathode layer 21,use of materials such as glass paste for adherence of the electrodelayers can be omitted, which do not participate in the cell reaction ordisturb the cell reaction. Accordingly, efficiency of the cell reactioncan be enhanced.

[0036] Similarly, the adhering anode layer 31 enhances adhesion of thefuel electrode 30 to the solid electrolyte layer 10 more effectively,and forms the three-phase interface contributing to more cell reactionsin the interface between the fuel electrode 30 and the solid electrolytelayer 10. Furthermore, the electricity collecting anode layer 32enhances electricity collecting performance more effectively, andsupplies the reactive gas more effectively by the reaction field wherethe cell reaction occurs. When single cells are integratedtwo-dimensionally to form a cell plate, and when the cell plates arefurther laminated, electric resistance between the single cells andelectric resistance between the cell plates can be reduced with theenhancement of the electricity collecting performance of the electrode.

[0037] Descriptions for the air electrode 20 and the fuel electrode 30will be made more concretely below.

[0038] First, in the single cell of this embodiment, the electricitycollecting cathode layer 22 should have a thickness thicker than that ofthe adhering cathode layer 21. This is because since the adheringcathode layer 21 is a dense film, it is difficult for the reactive gasto reach the three-phase interface when the thickness of the adheringcathode layer 21 is too thick. On the other hand, with respect to theelectricity collecting cathode layer 22, this is because since it isnecessary to decrease resistance of the electricity collecting cathodelayer 22 sufficiently in order to collect electricity, the electricitycollecting cathode layer 22 must have a thick thickness to some degree.

[0039] To be concrete, a ratio (tc1/tc2) of the thickness (tc1) of theadhering cathode layer 21 to the thickness (tc2) of the electricitycollecting cathode layer 22 should range from 1/1000 to 1/500.Furthermore, the thickness of the adhering cathode layer 21 should beequal to 1 μm or less, and the thickness of the electricity collectingcathode layer 22 should be equal to 10 μm or more.

[0040] Similarly, a ratio (ta1/ta2) of a thickness (ta1) of the adheringanode layer 31 to a thickness (ta2) of the electricity collecting anodelayer 32 should range from 1/1000 to 1/500. Furthermore, the thicknessof the adhering anode layer 31 should be equal to 1 μm or less, and thethickness of the electricity collecting anode layer 32 should be equalto 10 μm or more.

[0041] Furthermore, the adhering cathode layer 21 and the adhering anodelayer 31 (hereinafter referred to as “adhering electrode layers (21,31)”) should be formed of a conductive material having a particlediameter of 0.5 μm or less, and the electricity collecting cathode layer22 and the electricity collecting cathode layer 32 (hereinafter referredto as “electricity collecting electrode layers (22, 32)”) should beformed of a material containing a conductive material having a particlediameter of 0.8 Am or more. When the particle diameter of the conductivematerial of the adhering electrode layers (21, 31) is made small, adensity of contact points of the solid electrolyte layer 10 and theadhering electrode layers (21, 31) increases. Therefore, adhesion of theadhering electrode layers (21, 31) to the solid electrolyte layer 10 isimproved. The increase in the density of the contact points increases asubstantial area of the three-phase interface. Furthermore, by makingthe particle diameter of the conductive material of the electricitycollecting electrode layers (22, 32) larger, porosity more increases,and permeability of the reactive gas can be increased. Accordingly,since the reactive gas can be supplied to the three-phase interfaceeffectively, the cell reaction can be improved.

[0042] Furthermore, the adhering electrode layers (21, 31) should bediscontinuous thin film layers. Here, the discontinuous thin film layermeans a layer that is not a continuous thin film and not uniformlydense. In other words, the discontinuous thin film is a film showing astate where all portions of surfaces of individual particles do notnecessarily contact others perfectly but the individual particles haveportions that do not contact others. If the adhering electrode layers(21, 31) are continuous thin films that are uniformly dense, there is noroom for the reactive gas to enter, and it is impossible to form thethree-phase interface necessary for the cell reaction.

[0043] Furthermore, the electricity collecting electrode layers (22, 32)should adopt a three dimensional network structure or column structurein which individual constituent particles contact others and have porestherein. The network structure should be preferably adopted because thenetwork structure secures a larger contact area of the reactive gas withthe electrode layers and guarantees the electrical electricitycollecting function. In addition, the network structure can promotepermeability of the reactive gas.

[0044] Further, the electricity collecting electrode layers (22, 32)should have a ratio of the pores to the total volume (i.e. porosity),which ranges from 30 to 70 vol %. When the electricity collectingelectrode layers (22, 32) contains the pores at this ratio, it ispossible to secure good gas permeability. If the porosity is less than30 vol %, the gas permeability is disturbed, and if the porosity is morethan 70 vol %, a film strength may be insufficient. Also, such a poreshould have a size of about 0.1 to 5 μm which is suitable forelectrochemical reaction.

[0045] The electricity collecting electrode layers (22, 32) should becovered on the upper surface of the adhering electrode layers (21, 31)almost in a net form. By covering the layers (22, 32) on the adheringelectrode layers (21, 31), it is possible to relax thermal distortion.

[0046] Note that as the foregoing solid electrolyte layer 10, it shouldbe preferable to use one having a thickness of 100 μm or less. With theuse of the solid electrolyte layer 10 having the thickness of 100 μm orless, a desired energy conversion efficiency can be achieved easily.When the thickness of the solid electrolyte layer 10 exceeds 100 μm, itsspecific resistance becomes larger, and the energy conversion efficiencyis apt to be deteriorated.

[0047] Here, as a material of the adhering anode layer of the fuelelectrode, any one of nickel (Ni); nickel-chromium (Cr) alloy;nickel-iron (Fe) alloy; metals which are combinations of any of thesematerials; and nickel oxide (NiO and Ni complex oxide) can be used. As amaterial of the electricity collecting anode layer of the fuelelectrode, Ni. Ni—Cr, Ni—Fe, Pt, Ag, Ni—Cr—W—Mo alloy and Ni—Cr—Fe alloycan be used.

[0048] As a material of the adhering cathode layer of the air electrode,any one of silver (Ag), platinum (Pt), gold (Au), titanium (Ti),tungsten (W), lanthanum (La), strontium (Sr), cobalt (Co), iron (Fe),manganese (Mg) and chromium (Cr) can be used. Moreover, alternatively,combinations of any of these metals can be used. Still furthermore, anyone of La_(0.3)Co_(0.7)O₃, La_(0.7)Sr_(0.3)CrO₃, La_(0.3)Sr_(0.3 FeO) ₃,La_(0.7)Sr_(0.3)MnO₃and La_(0.7)Sr_(0.3)CrO₃ containing lanthanumcomplex oxide which is combinations of any of these can be alternativelyused. Further, as a material of the electricity collecting cathode layerof the air electrode, Ag, Pt or Au and one containing metals which arecombinations of any of these can be used.

[0049] Moreover, as the solid electrolyte layer, a material providingoxygen ion conductivity, for example, stabilized zirconia doped withneodium oxide (Nd₂O₃), samarium oxide (Sm₂O₃), yttria (Y₂O₃), gadoliniumoxide (Gd₂O₃) and the like; ceria (CeO₂) series solid solution; bithmusoxide, and LaGaO₃ can be used. However, the material of the solidelectrolyte layer is not limited to these materials.

[0050] Next, a method of manufacturing the single cell for the fuel cellof the first embodiment of the present invention will be described.

[0051] According to the method of manufacturing the single cell of thefirst embodiment of the present invention, the adhering cathode layerand the adhering anode layer are respectively formed on one surface andthe other surface of the solid electrolyte layer by use of a vacuum filmformation method. Subsequently, the electricity collecting cathode layeris formed on the adhering cathode layer by use of a printing method or aspray coating method. The electricity collecting anode layer is formedon the adhering anode layer by use of the printing method or the spraycoating method. Thereafter, the aggregate of these layers are baked, toobtain the single cell for the fuel cell.

[0052] According to the above method of the single cell, since theadhering cathode layer and the adhering anode layer are respectivelyformed by use of the vacuum film formation method, these films are madeto be a dense thin film having an excellent adhering function. Inaddition, since the electricity collecting cathode layer and theelectricity collecting anode layer are formed by use of the printingmethod or the spray coating method, it is possible to easily form acomparatively porous and thick film. Accordingly, this manufacturingmethod is suitable for a fabrication method of the single cell of thefirst embodiment.

[0053] According to another method of manufacturing a single cell of thefirst embodiment of the present invention, the materials for forming theadhering cathode layer and the adhering anode layer are respectivelycovered on one surface and the other surface of the solid electrolytelayer by use of the spray coating method, and baked, thus forming theadhering cathode layer and the adhering anode layer. Furthermore, theelectricity collecting cathode layer and the electricity collectinganode layer are respectively covered on the adhering cathode layer andthe adhering anode layer by use of the printing method or the spraycoating method, and then baked, thus forming the electricity collectingcathode layer on the adhering cathode layer and the electricitycollecting anode layer on the adhering anode layer respectively. Thus,the single cell according to another embodiment of the present inventionis fabricated. According to this method, since the adhering electrodelayers and the electricity collecting electrode layers can be formed inthe same process, the manufacture of the single cell is made easier.

Second Embodiment

[0054] A structure of a single cell according to a second embodiment ofthe present invention is shown in FIG. 2. Air electrode 25 is formed onone surface of the solid electrolyte layer 10, and a fuel electrode 35is formed on the other surface thereof. The air electrode 25 have anadhering cathode layer 23 and an electricity collecting cathode layer24.

[0055] In the single cell of the second embodiment, an ion electronconduction film providing electron conductivity and ion conductivity isused as the adhering cathode layer 23 and the electricity collectingcathode layer 24 of the air electrode 25, and electrode performance ofthe air electrode 25 is enhanced. Moreover, as the adhering cathodelayer 23, silver (Ag), a material essentially containing silver (Ag),bismuth oxide (Bi), or a material essentially containing the bismuthoxide is used.

[0056] Since Ag and bismuth oxide exhibit the electron conductivity andthe ion conductivity and have a low melting point, the air electrode canbe adhered to the solid electrolyte layer at a low temperature.Accordingly, since a temperature required to form the air electrode canbe decreased, a high temperature reaction between the electrode and thesolid electrolyte layer can be suppressed. A material such as LSC can beused as the electricity collecting cathode layer 24, and good adhesionand conductivity can be secured.

[0057] When Ag or a material essentially containing Ag is used as theadhering cathode layer 23, the electricity collecting cathode layer 24should contain one of nickel (Ni), nickel-chromium (Ni—Cr) alloy andnickel-iron (Ni—Fe) alloy; combinations of any of these materials.Alternatively, the electricity collecting cathode layer 24 shouldcontain nickel oxide and one of silver (Ag), platinum (Pt), gold (Au),titanium (Ti), tungsten (W), lanthanum (La), strontium (Sr), cobalt(Co), iron (Fe), manganese (Mn), chromium (Cr) and combinations of anyof these metals. Otherwise, the electricity collecting cathode layer 24should contain one of La_(0.3)Co_(0.7)O₃, La_(0.7)Sr_(0.3)CrO₃,La_(0.7)Sr₀₃FeO₃, La_(0.7)Sr_(0.3)MnO₃. and La_(0.7)Sr_(0.3)CrO₃; or onecontaining lanthanum complex oxide which is a combination of any ofthese.

[0058] Furthermore, when bismuth oxide and a material essentiallycontaining the bismuth oxide is used as the adhering cathode layer 23,the electricity collecting cathode layer 24 should contain at least onemetal selected from the group consisting of silver, platinum, gold,titanium, tungsten, lanthanum, strontium, cobalt, iron, manganese andchromium. Alternatively, the electricity collecting cathode layer 24should contain lanthanum complex oxide selected from the groupconsisting of La_(0.3)Co_(0.7)O₃, La_(0.7)Sr_(0.3)CrO₃,La_(0.7)Sr_(0.3)FeO₃, La_(0.7)Sr_(0.3)MnO₃ and La_(0.7)Sr_(0.3)CrO₃.

[0059] Resistance of the adhering cathode layer 23 should be equal to10% of the total resistance of the single cell or less.

[0060] It is preferable to constitute the single cell so that the filmthickness tc1 of the adhering cathode 23 and the average particlediameter dc of the constituent particles of the air electrode 25 have acertain relation between them. In this case, when the single cell isconstituted so as to create such a relation between them, adhesion ofthe solid electrolyte layer and the electrode can be enhancedeffectively without decreasing the cell performance.

[0061] A single cell structure should be adopted, which satisfies, forexample, a relation expressed by tc1≦dc where tc1 is the film thicknessof the adhering cathode layer and dc is the average particle diameter ofthe foregoing electrode constituent particles. Note that in the case oftc1>dc, a gas diffusion property within the electrode is deterioratedand an electrical output of the single cell may be lowered.

[0062] Also, a single cell structure should be adopted, which satisfiesa relation expressed by 0.01 dc≦tc1≦0.5 dc where tc1 is the filmthickness of the adhering cathode layer and dc is the average particlediameter of the foregoing electrode constituent particles. Note that inthe case of tc1>0.5 dc, a gas diffusion property within the electrode isdeteriorated and an electrical output of the single cell may be lowered,in the case of tc1<0.01 dc, an adhesion effect may be insufficient.

[0063] Furthermore, the average diameter dc of general electrodeconstituent particles should be about 0.5 to 50 μm in terms of electrodeperformance and easiness of handling. Accordingly, the foregoing filmthickness tc1 should be set to 0.1 μm ≦tc1≦5 μm. Note that in the caseof tc1>5 μm, the gas diffusion property within the electrode isdeteriorated and the electrical output of the single cell may belowered, and in the case of tc1<0.1 μm, the adhesion efficiency may beinsufficient.

[0064] The second embodiment in which the air electrode alone is formedby the adhering cathode layer and the electricity collecting cathodelayer is described in the above. However, also the fuel electrode may beconstituted by the adhering anode layer and the electricity collectinganode layer. In this case, the relation between the film thickness tc1of the adhering cathode layer of the air electrode and the averageparticle diameter dc of the constituent particles, which are describedin the above, can be similarly applied to the fuel electrode.

[0065] Specifically, a single cell structure should be adopted, whichsatisfies a relation expressed by ta1≦da where ta1 is the film thicknessof the adhering anode layer of the fuel electrode, and the da is theaverage particle diameter of the particles of the fuel electrode.Furthermore, a single cell structure should be adopted, which satisfiesa relation expressed by 0.01 da≦ta1≦0.5 da where ta1 is the filmthickness of the adhering anode layer of the fuel electrode and da isthe average particle diameter of the particles of the fuel electrode.Still furthermore, the average particle diameter da of the constituentparticles of the fuel electrode should be about 0.5 to 50 μm, and thefilm thickness ta1 of the adhering anode layer should satisfy therelation expressed by 0.1 μm ≦ta1≦5 μm.

[0066] Next, a method of manufacturing the air electrode 25 of thesingle cell according to the second embodiment will be described.

[0067] This manufacturing method comprises a step (I) of forming aadhering cathode layer on a solid electrolyte layer, a step (II) ofcoating an electricity collecting cathode layer onto the adheringcathode layer, and a step (IID of baking the solid electrolyte layer andan air electrode material to adhere the air electrode material and thesolid electrolyte layer to each other.

[0068] Here, in the step (I) of forming the adhering cathode layer onthe foregoing solid electrolyte layer, a PVD method and a wet filmformation method can be adopted. As the PVD method, there are, forexample, a sputtering method, an EB deposition method, a laser beamabrasion method and the like. Moreover, as the wet film formationmethod, there are a printing method, a spray coating method, a sol-gelmethod, a plating method and the like.

[0069] Furthermore, in the step (III) of baking the solid electrolytelayer and the air electrode material to adhere the solid electrolytelayer and the air electrode material to each other, a bakingtemperature, that is, a heat treatment temperature at which the solidelectrolyte layer and the air electrode are adhered to each other by theadhering cathode layer should be set to a range of 700 to 1000° C. Inthe temperature of less than 700° C., a single cell may be damagedduring an operation. In the temperature 1000° C. or more, the materialforming the adhering cathode layer becomes too soft, and the electrodematerial may move to cohere.

[0070] Furthermore, since the low melting point material such as Ag andbismuth oxide is used as the adhering cathode layer in the above baking,the baking is effective since the baking can be performed at atemperature which is lower by 200° C. or more than the lowesttemperature among sintering temperatures for synthesizing respectivematerial powders of the air electrode, the fuel electrode and the solidelectrolyte layer. Note that the baking is performed at a temperatureexceeding this temperature, a diffusion reaction proceeds between thesolid electrolyte layer and the air electrode, a reaction product isformed at an interface between the solid electrolyte layer and the airelectrode, and a cell output of the single cell may be lowered.

[0071] To be concrete, for example, a Ag film of a thickness of 2 to 3μm is formed on the solid electrolyte layer formed of YSZ by use of thesputtering method, LSC powders are covered on the Ag film, and then theyare baked at 850° C. Thus, the air electrode can be formed. By adoptingsuch a manufacturing method, the single cell for the fuel cell which hasexcellent electricity generation performance and durability can beobtained.

[0072] There is no special limitation as to a manufacturing method ofthe fuel electrode. However, when the fuel electrode is constituted bythe adhering anode layer and the electricity collecting anode layer, theforegoing manufacturing method of the air electrode can be appliedthereto.

Cell Plate for Fuel Cell and Fuel Cell

[0073] Although a structure obtained by laminating the plurality ofsingle cells of the first and second embodiments of the presentinvention can be used as the fuel cell, the plurality of single cellsare arranged two-dimensionally, and then these single cells areprocessed to a united cell plate. A structure obtained by laminating theplurality of cell plates can be also used as the fuel cell.

[0074]FIG. 3A is a partial section view showing an example of a cellplate for a fuel cell of an embodiment of the present invention, andFIG. 3B is a perspective view of FIG. 3A. As shown in FIG. 3A, in thecell plate, the plurality of openings 60 are provided in the substrate50, and a single cell for a fuel cell composed of the solid electrolytelayer 10, the fuel electrode 20 and the air electrode 30 is arranged ineach of the openings 60. As shown in FIG. 3A, when the plurality ofsingle cells are arranged on the single common substrate 50, there is amerit that the solid electrolyte layer 10 of each single cell can beformed with a thin film.

[0075] Note that the fuel electrode 20 may be disposed under the solidelectrolyte layer 10 and the air electrode 30 may be disposed on thesolid electrolyte layer 10. In addition, any of the solid electrolytelayer 10, the fuel electrode 20 and the air electrode 30 may be used asa supporting plate without use of the substrate 50.

[0076] Furthermore, when the fuel cell is fabricated by laminating thesingle cells or the cell plates, the fuel electrode and the airelectrode in each single cell or each cell plate must be arranged so asto contact flow paths of the reactive gas corresponding thereto. Theplurality of single cells and the plurality of cell plates may belaminated so as to allow the fuel electrode to face another fuelelectrode and to allow the air electrode to face another air electrode.In addition, in order to secure the flow path of the reactive gas, aseparator may be interposed between the cell plates, if necessary.

[0077] To manufacture the solid oxide fuel cell, inorganic adhesive iscoated onto surfaces of the plurality of the single cells or the cellplates, and a predetermined number of the single cells or the cellplates are laminated. Thereafter, the plurality of the single cells orthe cell plates adhered, which are laminated, may be adhered to eachother by pressurizing and heating.

EXAMPLES

[0078] Examples and comparative examples of the present invention willbe described below.

[0079] In the examples and the comparative examples described below, thesingle cell for the fuel cell was fabricated, and performance evaluationfor the single cell obtained was performed as described below.

Performance Evaluation Method

[0080] 1. Tape Peeling-off Test Conditions

[0081] Scotch™ tape (manufactured by 3M Co. Ltd., type: Mending Tape810) was pasted on the surface of the single cell, and the surface ofthe single cell on which the tape was pasted was pulled with force of500 g at an angle of 45° relative to the surface of the single cell.When the peeling of the surface of the single cell did not occur, theevaluation was sorted to “◯” (Good).

[0082] 2. Cell Property Evaluation Conditions

[0083] Cell properties of the fuel cell constituted by use of the singlecell of each example were measured under the conditions that temperaturewas 700° C., fuel gas was hydrogen, oxidation gas was air, and gaspressure was 1 atm.

[0084] Note that measurements of the cell properties as to the examples3 to 5 and the comparative examples 4 to 7 were performed under theconditions that an open voltage was 0.95 V and a maximum output was 0.11W/cm².

[0085] 3. Resistance Evaluation Conditions

[0086] As to the examples 3 to 5 and the comparative examples 4 to 7, asthe resistance of the single cell and the resistance as to the adheringcathode layer, an AC impedance value at 700° C. was measured.

Fabrication of the Single Cell for the Fuel Cell Example 1

[0087] As shown in FIG. 4A, the single cell of the example 1 has the airelectrode 20A composed of the adhering cathode layer 21A and theelectricity collecting cathode layer 22A, which are formed on onesurface of the solid electrolyte layer 10A and the fuel electrode 30Acomposed of the adhering anode layer 31A and the electricity collectingcathode layer 32A, which are formed on the other surface of the solidelectrolyte layer 10A.

[0088] To be concrete, a zirconia sintered body containing yttria of 8mol % (hereinafter referred to as “YSZ sintered body”), which has athickness of 80 μm was used as the electrolyte layer, Ag was used as theair electrode, and Ni was used as the fuel electrode.

[0089] First, as the adhering cathode layer, a Ag layer having athickness of 50 nm was formed on the upper surface of the plane-shapedYSZ sintered body by use of a rf sputtering method. A Ni layer having athickness of 50 nm was formed on the lower surface of the YSZ sinteredbody by use of the sputtering method. Ar was used as sputtering gas, andgas pressure was set to 0.1 Pa. Sputtering power was set to 200 W.

[0090] Next, as the electricity collecting cathode layer, Ag pastecontaining Ag particles of a particle diameter of 8 μm was coated ontothe adhering cathode layer to a thickness of about 30 μm by use of thespray coating method.

[0091] As the electricity collecting anode layer, Ni paste containing Niparticles of a particle diameter of 5 μm was coated onto the adheringcathode layer to a thickness of about 50 μm by use of the spray coatingmethod. Here, as the sprayed paste, a compound was used, which isobtained by mixing Ag powders and Ni powders into a vehicle formed ofbutyl-carbitol (91.5) and ethyl cellulose (8.5) with a weight ratio of1:2.5.

[0092] Thereafter, the YSZ sintered body in which each electrode layerwas formed was baked at 600° C. A thickness of the electricitycollecting cathode layer of the air electrode after baking was 15 μm,and a thickness of the electricity collecting anode layer of the fuelelectrode was 35 μm.

[0093] The constitution of the electrode and the evaluation results areshown in Table 1 of FIG. 5.

[0094] Note that the adhering cathode layer of the air electrode of thesingle cell in the example 1 was a discontinuous film formed ofparticles having a particle diameter of 0.05 μm, a porosity of the Agfilm in the electricity collecting cathode layer of the air electrodewas 50%, and a porosity of the Ni film thereof was 45%, and theparticles partially contacted with each other in the adhering cathodelayer.

[0095] In the single cell of the example 1, the tape peeling test showedgood adhesion. Moreover, the cell property was improved by about 8%compared to the fuel cell using the single cell obtained in thecomparative example 1 to be described later.

[0096] Comparative Example 1

[0097] As shown in FIG. 4B, the single cell of the comparative example 1has the single-layered air electrode 200A formed on one surface of thesolid electrolyte layer 100 and the fuel electrode 300A having asingle-layered structure, which is formed on the other surface of thesolid electrolyte layer 100.

[0098] The air electrode and the fuel electrode were formed by use ofpaste obtained by adding glass adhesive to Ag and Ni. The single cell ofthe comparative example 1 was fabricated by use of the same conditionsas those of example 1 other than those under which the air electrode andthe fuel electrode were formed.

[0099] To be concrete, as the air electrode, an Ag layer having athickness of about 50 μm was formed on one surface of the YSZ sinteredbody by use of the spray coating method. As the fuel electrode, a Nilayer having a thickness of about 50 μm was formed on the other surfaceof the YSZ sintered body by use of the same spray coating method.

[0100] As the sprayed paste, a compound was used, which was obtained bymixing Ag powders and Ni powders into a vehicle formed of butyl-carbitol(91.5) and ethyl cellulose (8.5) with a weight ratio of 1:2.5 and byadding borosilicate glass offering softening temperature of 390° C. toAg and Ni by 4%.

[0101] Thereafter, the YSZ sintered body onto which the Ag layer and theNi layer were coated was baked in the atmosphere at temperature of 600°C. The thickness of the Ag layer after baking was 15 μm, and thethickness of the Ni layer after baking was 35 μm. The constitution ofthe electrode and the evaluation results are shown in Table 1 of FIG. 5.

[0102] The single cell of the comparative example 1 showed good adhesionin the tape peeling test. Moreover, with regard to the cell property, acell output of 0.12 W/cm² hour (i=0.4 A/cm² hour) was obtained.

Example 2

[0103] The fundamental structure of the single cell of the example 2 isthe same as that shown in FIG. 4A similarly to the single cell of theexample 1. The single cell of the example 2 was fabricated under thesame conditions as those of the example 1 except that the adheringcathode layer of the air electrode and the adhering anode layer of thefuel electrode were formed by use of the spray coating method.

[0104] To be concrete, as the adhering cathode layer, a Ag layer havinga thickness of 0.5 μm was formed on one surface of the YSZ sintered bodyby use of the spray coating method. Similarly, as the adhering anodelayer, a Ni layer having a thickness of 0.5 μm was formed on the othersurface of the YSZ sintered body by use of the spray coating method.Thereafter, the adhering cathode layer and the adhering anode layer werebaked in the atmosphere at temperature of 800° C. Thus, the respectivethicknesses of the adhering cathode layer and the adhering anode layerwere made equal to 0.1 μm.

[0105] Next, with Ag paste containing Ag particles of a particlediameter of 8 μm, the electricity collecting cathode layer having thethickness of about 30 μm was formed on the adhering cathode layer (Agsprayed layer) by use of the spray coating method. Moreover, with Nipaste containing Ni particles of a particle diameter of 5 μm, theelectricity collecting anode layer having the thickness of about 50 μmwas formed on the adhering anode layer (Ni sprayed layer) by use of thespray coating method.

[0106] As the sprayed paste, a compound was used, which was obtained bymixing Ag powders and Ni powders into a vehicle formed of butyl-carbitol(91.5) and ethyl cellulose (8.5) with a weight ratio of 1:5. Moreover,Ag used for this paste has a particle diameter of 0.3 μm and 1 μm, andNi was used as fine powders having a particle diameter of 0.7 μm.

[0107] Thereafter, the YSZ sintered body on which the sprayed film wasformed was baked in the atmosphere at temperature of 600° C. Withrespect to the thickness of the adhering cathode layer after baking, thethickness of the Ag layer was 15 μm, and the thickness of the Ni layerwas 35 μm. The constitution of the electrode and the evaluation resultsare shown in Table 1.

[0108] Note that the adhering cathode layer and the adhering anode layerwere a discontinuous film formed of conductive particles having aparticle diameter of 0.3 to 0.5 μm, a porosity of the electricitycollecting cathode layer (Ag film) was 50%, and a porosity of theelectricity collecting anode layer (Ni film) was 45%, and the particlespartially contacted with each other in the adhering cathode layer.

[0109] In the single cell of the example 2, the tape peeling test showedgood adhesion. Moreover, the cell property was improved by about 6%compared to the fuel cell using the single cell obtained in thecomparative example 1.

[0110] Comparative Example 2

[0111] The fundamental structure of the single cell of the comparativeexample 2 is the same as that shown in FIG. 4B similarly to the singlecell of the comparative example 1. The single cell of the comparativeexample 2 was fabricated under the same conditions as those of theexample 1 except that an electrode having a single-layered structure wasformed.

[0112] To be concrete, Ag paste containing Ag particles of a particlediameter of 8 μm was formed on one surface of the YSZ sintered body byuse of the spray coating method, thus forming the air electrode having athickness of about 30 μm. Moreover, Ni paste containing Ni particles ofa particle diameter of 5 μm was formed on the other surface of the YSZsintered body by use of the spray coating method, thus forming the fuelelectrode having a thickness of about 50 μm.

[0113] As the sprayed paste, a compound was used, which was obtained bymixing Ag powders and Ni powders into a vehicle formed of butylcarbitol(91.5) and ethyl cellulose (8.5) with a weight ratio of 1:2.5.

[0114] The YSZ sintered body on which the sprayed film was formed wasbaked in the atmosphere at temperature of 600° C. With respect to thethickness of the sprayed film after baking, the thickness of the Aglayer was 15 μm, and the thickness of the Ni layer was 35 μm. Theconstitution of the electrode and the evaluation results are shown inTable 1 of FIG. 5.

[0115] Note that in the foregoing sprayed film, the Ag layer (airelectrode) showed porosity of 50%, the Ni layer (fuel electrode) showedporosity of 45% and the particles partially contacted with each other.

[0116] In the single cell of the comparative example 2, the tape peelingtest showed partial peeling, and did not show sufficient adhesion.Moreover, the cell property was improved by about 3% compared to thefuel cell using the single cell obtained in the comparative example 1.This is because no intervention substance such as a glass adhesionmaterial disturbing the cell reaction exists at the interface betweenthe electrolyte and the electrode.

[0117] Comparative Example 3

[0118] The fundamental structure of the single cell of the comparativeexample 3 is shown in FIG. 4C. Similarly to the single cell of theexample 1, the air electrode 200B and the fuel electrode 300B adopt thedouble-layered structure similarly to that of the example 1,respectively. However, the conditions as the film thickness of thesingle cell are different from those of the example 1. Thickness of thelayers (210, 310) corresponding to the adhering electrode layers of theexample 1 was set to 2 μm. Conditions other than the conditions as tothe film thickness are the same as those of the single cell of theexample 1.

[0119] To be concrete, a Ag layer having a thickness of about 2 μm wasformed on one surface of the YSZ sintered body by use of a rf sputteringmethod, and a Ni layer having a thickness of about 2 μm was formed onthe other surface of the YSZ sintered body by use of the rf sputteringmethod. The constitution of the electrode and the evaluation results areshown in Table 1.

[0120] Note that in layers (220, 320) corresponding to the electricitycollecting electrode layer, the Ag film has porosity of 50%, and the Nifilm has porosity of 45%, and particles partially contact with eachother. Note that layers (210, 310) corresponding to the adheringelectrode layers were a continuous layer formed of particles having aparticle diameter of 0.1 to 0.5 μm.

[0121] Note that with regard to sputtering film formation conditions, Arwas used as sputtering gas, gas pressure was set to 0.05 Pa, andsputtering power was set to 800 W.

[0122] In the single cell of the comparative example 3, the tape peelingtest showed partial peeling, and did not show good adhesion. Moreover,the cell property decreased by about 10% compared to the fuel cell usingthe single cell obtained in the comparative example 1. The cell reactionat the interface between the electrolyte and the electrode did notproceed sufficiently.

Example 3

[0123] The structure of the single cell of the example 3 is shown inFIG. 4D. In the single cell of the example 3, a laminated structure wasused as the air electrode 25A composed of the adhering cathode layer 23Aand the electricity collecting cathode layer 24A. Moreover,La_(0.3)Co_(0.7)O₃ (LSC), which is a perovskite-type oxide electrodematerial, was used as the electricity collecting cathode layer 24A.

[0124] To be concrete, a plate of a sintered body formed of stabilizedzirconia to which Y₂O₃ is added by 8 mol % (hereinafter referred to as“8YSZ”), which has a thickness of 0.5 mm and a diameter of 15 mm, wasfirst prepared as the solid electrolyte layer 10A.

[0125] Next, as an air electrode material, a La_(0.3)Co_(0.7)O₃ (LSC)sintered body was made by mixing prescribed raw materials at aprescribed ratio and by baking them in accordance with an ordinarymanufacturing method of ceramics. Baking temperature was set to 1200° C.at this time. Thereafter, the LSC sintered body was ground by a ballmill, thus obtaining LSC powders having an average particle diameter of5 μm.

[0126] As the adhering cathode layer 23A, a Ag layer having a thicknessof about 1 μm was formed on surface of the foregoing 8YSZ sintered bodyby use of the sputtering method. Next, slurry obtained by dispersing theprepared LSC powders into turpentine oil (solvent) was coated onto theAg layer that is the adhering cathode layer 23A, and the turpentine oilwas dried. Thereafter, baking was performed.

[0127] Moreover, Ni paste was coated onto the other surface of the 8YSZsintered body, and baked at 600° C., thus forming the fuel electrode35B. The constitution of the electrode and the evaluation results areshown in Table 2 of FIG. 6.

Example 4

[0128] The fundamental structure of the single cell of the example 4 isthe same as that of the example 3 shown in FIG. 4D. The same conditionsas those of the example 3 were used except that a bismuth oxide layerwas formed as the adhering cathode layer 23A of the air electrode. Notethat the bismuth oxide layer was formed by use of an EB depositionmethod. The constitution of the electrode and the evaluation results areshown in Table 2 of FIG. 6.

Example 5

[0129] The fundamental structure of the single cell of the example 5 isthe same as that of the example 3 shown in FIG. 4D. A mixed layer of Agand LSC was used as the adhering cathode layer 23A of the air electrode.Furthermore, a thickness of the adhering cathode layer was set to 0.1μm, and baking temperature was set to 800° C. The single cell wasfabricated by using the approximately same conditions as those of theexample 3 except the above. The constitution of the electrode and theevaluation results are shown in Table 2 of FIG. 6.

[0130] Comparative Example 4

[0131] The air electrode was formed in the form of the single layerstructure formed of LSC without providing the adhering cathode layer.The baking temperature was set to 1100° C. The single cell wasfabricated by using the approximately same conditions as those of theexample 3 except the above. The constitution of the electrode and theevaluation results are shown in Table 2 of FIG. 6.

[0132] Comparative Example 5

[0133] The air electrode was formed in the form of the single layerstructure formed of LSC without providing the adhering cathode layer.The single cell of the comparative example 5 was fabricated by using theapproximately same conditions as those of the example 3 except theabove. The constitution of the electrode and the evaluation results areshown in Table 2 of FIG. 6.

[0134] Comparative Example 6

[0135] The single cell of the comparative example 6 was fabricated byusing the approximately same conditions as those of the example 3 exceptthat a thickness of the adhering cathode layer was set to 10 μm and thebaking temperature was set to 850° C. The constitution of the electrodeand the evaluation results are shown in Table 2 of FIG. 6.

[0136] Comparative Example 7

[0137] The adhesive cathode layer was formed by bismuth oxide and glassfrit. Moreover, the adhering cathode layer having a thickness of 2 μmwas prepared by use of a printing method. The single cell of thecomparative example 7 was fabricated by using the approximately sameconditions as those of the example 3 except that the baking temperaturewas set to 500° C. The constitution of the electrode and the evaluationresults are shown in Table 2 of FIG. 6.

[0138] As is understood based on Table 2, it is proved that the singlecell and the fuel cell obtained in the examples 3 to 5 are excellent inthe adhesion property and the cell resistance. On the other hand, it isproved that the single cell and the fuel cell obtained in thecomparative examples 4 to 7 offer deteriorated adhesion property andhigh cell resistance because a conductive adhering layer is not used andthe baking temperature is outside the preferable range of the presentinvention.

[0139] As described above, according to the present invention, since theelectrodes (fuel electrode and air electrode) are formed in thelaminated structure and the respective function is assigned to eachlayer constituting the lamination structure, it is possible to providethe single cell and the cell plate which offer low electrical resistanceand good adhesion property and can take a large three-phase interface.Furthermore, the present invention can provide the method ofmanufacturing the same and the solid oxide fuel cell comprising thesame.

[0140] The entire contents of Japanese Patent Applications P2001-9394(filed on Jan. 17, 2001) and P2001-144550 (filed on May 14, 2001) areincorporated herein by reference. Although the inventions have beendescribed above by reference to certain examples of the inventions, theinventions are not limited to the examples described above.Modifications and variations of the examples described above will occurto those skilled in the art, in light of the above teachings. Forexample, in the present invention, the shape and the like of the singlecell and the cell plate can be selected arbitrarily, and the fuel cellin accordance with an objective output can be fabricated. Moreover, theair electrode and the fuel electrode can be formed also to a layeredstructure composed of more layers without limitation to the two-layeredstructure.

[0141] The scope of the inventions is defined with reference to thefollowing claims.

What is claimed is:
 1. A single cell, comprising: (a) a solidelectrolyte layer; (b) an air electrode comprising: an adhering cathodelayer formed on one surface of the solid electrolyte layer andconfigured to show a function to allow the air electrode and the solidelectrolyte layer to adhere electrically and mechanically to each other;and an electricity collecting cathode layer formed on the adheringcathode layer and configured to show an electricity collecting functionof the air electrode; and (c) a fuel electrode formed on the othersurface of the solid electrolyte layer, wherein the adhering cathodelayer has a structure denser than the electricity collecting cathodelayer, and configures a three-phase interface composed of the solidelectrolyte layer, reactive gas and the air electrode or a two-phaseinterface composed of the solid electrolyte layer and the air electrode,and the electricity collecting cathode layer is thicker than theadhering cathode layer, and has pores providing the reactive gas to thethree-phase interface or the two-phase interface.
 2. A single cell,comprising: (a) a solid electrolyte layer; (b) an air electrode formedon one surface of the solid electrolyte layer; and (c) a fuel electrodecomprising: an adhering anode layer formed on the other surface of thesolid electrolyte layer and configured to show a function to allow theair electrode and the solid electrolyte layer to adhere electrically andmechanically to each other; and an electricity collecting anode layerformed on the adhering anode layer and configured to show an electricitycollecting function, wherein the adhering anode layer has a structuredenser than the electricity collecting anode layer, and configures athree-phase interface composed of the solid electrolyte layer, reactivegas and the fuel electrode, and the electricity collecting anode layeris thicker than the adhering anode layer, and has pores providing thereactive gas to the three-phase interface.
 3. The single cell accordingto claim 1, wherein the adhering cathode layer comprises a conductiveparticle material having a particle diameter of 0.5 μm or less; and theelectricity collecting cathode layer comprises a conductive particlematerial having a particle diameter of 0.8 μm or more.
 4. The singlecell according to claim 1, wherein the adhering cathode layer is adiscontinuous thin film layer; and the electricity collecting cathodelayer has conductive particles forming a three-dimensional networkstructure.
 5. The single cell according to claim 1, wherein a ratio(tc1/tc2) of a thickness (tc1) of the adhering cathode layer to athickness (tc2) of the electricity collecting cathode layer ranges from1/1000 to 1/500.
 6. The single cell according to claim 1, wherein thethickness (tc1) of the adhering cathode layer is equal to 1 μm or less,and the thickness (tc2) of the electricity collecting cathode layer isequal to 10 μm or more.
 7. The single cell according to claim 1, whereinthe electricity collecting cathode layer has pores at a rate of 30 to 70vol % of a total volume.
 8. The single cell according to claim 1,wherein the electricity collecting cathode layer is coated on theadhering cathode layer approximately in a net fashion.
 9. The singlecell according to claim 1, wherein the thickness (tc1) of the adheringcathode layer and an average diameter (dc) of constituent particles ofthe air electrode satisfy a relation of tc1≦dc.
 10. The single cellaccording to claim 1, wherein the thickness (tc1) of the adheringcathode layer and an average diameter (dc) of constituent particles ofthe air electrode satisfy a relation of 0.01 dc≦tc1≦0.5 dc.
 11. Thesingle cell according to claim 1, wherein the thickness (tc1) of theadhering cathode layer is within a range of 0.1 μm≦tc1≦5 m.
 12. Thesingle cell according to claim 1, wherein the adhering cathode layer isformed of silver or essentially contains silver.
 13. The single cellaccording to claim 12, wherein the electricity collecting cathode layeressentially contains: at least one metal selected from the groupconsisting of silver, platinum, gold, titanium, tungsten, lanthanum,strontium, cobalt, iron, manganese and chromium; or at least onelanthanum complex oxide selected from the group consisting ofLa_(0.3)Co_(0.7)O₃La_(0.7)Sr_(0.3)CrO₃, La_(0.7)Sr_(0.3)FeO₃,La_(0.7)Sr_(0.3)MnO₃ and La_(0.7)Sr_(0.3)CrO₃.
 14. The single cellaccording to claim 1, wherein the adhering cathode layer is formed ofbismuth oxide or essentially contains bismuth oxide.
 15. The single cellaccording to claim 14, wherein the electricity collecting cathode layeressentially contains: at least one metal selected from the groupconsisting of silver, platinum, gold, titanium, tungsten, lanthanum,strontium, cobalt, iron, manganese and chromium; or at least onelanthanum complex oxide selected from the group consisting ofLa_(0.3)Co_(0.7)O₃, La_(0.7)Sr_(0.3), CrO₃, La_(0.7)Sr_(0.3 FeO)₃La_(0.7)Sr_(0.3)MnO₃ and La_(0.7)Sr_(0.3)CrO₃.
 16. The single cellaccording to claim 2, wherein the adhering anode layer containsconductive particles having a particle diameter of 0.5 μm or less; andthe electricity collecting anode layer contains conductive particleshaving a particle diameter of 0.8 μm or more.
 17. The single cellaccording to claim 2, wherein the adhering anode layer is adiscontinuous thin film layer; and the electricity collecting anodelayer has conductive particles forming a three-dimensional networkstructure.
 18. The single cell according to claim 2, wherein a ratio(ta1/ta2) of a thickness (ta1) of the adhering anode layer to athickness (ta2) of the electricity collecting cathode layer ranges from1/1000 to 1/500.
 19. The single cell according to claim 2, wherein thethickness (ta1) of the adhering anode layer is equal to 1 μm or less,and the thickness (ta2) of the electricity collecting anode layer isequal to 10 μm or more.
 20. The single cell according to claim 2,wherein the electricity collecting anode layer has pores at a rate of 30to 70 vol % of a total volume.
 21. The single cell according to claim 2,wherein the electricity collecting anode layer is coated on the adheringanode layer approximately in a net fashion.
 22. The single cellaccording to claim 2, wherein the thickness (ta1) of the adhering anodelayer and an average diameter (da) of constituent particles of the fuelelectrode satisfy a relation of ta1≦da.
 23. The single cell according toclaim 2, wherein the thickness (ta1) of the adhering anode layer and anaverage diameter (da) of constituent particles of the fuel electrodesatisfy a relation of 0.001 da≦ta1≦0.5 da.
 24. The single cell accordingto claim 2, wherein the thickness (ta1) of the adhering anode layer iswithin a range of 0.1 μm≦ta1≦5 μm.
 25. The single cell according toclaim 2, wherein the adhering anode layer contains at least one metalselected from the group consisting of nickel, nickel-chromium alloy andnickel-iron alloy, or nickel oxide.
 26. The single cell according toclaim 2, wherein the electricity collecting anode layer contains atleast one metal selected from the group consisting of nickel,nickel-chromium alloy and nickel-iron alloy, or nickel oxide.
 27. A cellplate for a fuel cell comprising: an plate-shaped body in which thesingle cells set forth in claim 1 arranged two-dimensionally to beunited.
 28. A cell plate for a fuel cell comprising: an plate-shapedbody in which the single cells set forth in claim 2 arrangedtwo-dimensionally to be united.
 29. A fuel cell comprising: layeredsingle cells, the single cell is set forth in claim
 1. 30. A fuel cellcomprising: layered single cells, the single cell is set forth in claim2.
 31. A fuel cell comprising: layered cell plates, the cell plate isset forth in claim
 27. 32. A fuel cell comprising: layered cell plates,the cell plate is set forth in claim
 28. 33. A method of manufacture ofa single cell comprising: forming a solid electrolyte layer; forming anadhering anode layer on one surface of the solid electrolyte layer andan adhering cathode layer on the other surface of the solid electrolytelayer, by use of one of a PVD method, a CVD method and a plating method;forming an electricity collecting anode layer on the adhering anodelayer and an electricity collecting cathode layer on the adheringcathode layer, by use of one of a spray coating method and a printingmethod; and baking a resultant one after formation of the electricitycollecting anode layer and the electricity collecting cathode layer. 34.The method according to claim 33, wherein the baking is performed withina temperature of 700 to 1000° C.
 35. The method according to claim 33,wherein the baking is performed within a temperature, the temperature islower by 200° C. or more than a temperature lowest among sinteringtemperatures at which materials of the adhering anode layer, theelectricity collecting anode layer, adhering cathode layer, electricitycollecting cathode layer, and a solid electrolyte layer are synthesized.